WSP05278

• File Number: 8200.760
• Description: Yampa River General
• State: CO
• Basin: Yampa/White
• Water Division: 6
• Date: 7/31/1990
• Author: Hydrosphere
• Title: Yampa River Basin - Alternatives Feasibility Study - Plan of Study
• Water Supply Pro - Doc Type: Report/Study

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Plan of Study
SUB-TASK 3b: CHARACfERIZE POTENTIAL SITES

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Purpose

In this sub-task various site-specific characteristics which would affect site developability will
be evaluated. Among the site characteristics to be considered are physical site inflows,
potential site storage volume and related factors, presence of known fatal geotechnical and
environmental flaws, recreation use potential, and the ability of a reservoir at the site to
deliver water to meet identified demands. Project costs will not be developed, although
factors that might imply large development costs, such as large fill volumes, will be
considered. The determination of each of these factors is described below. A summary
sheet describing these characteristics will be prepared for each site.

Approach

1) Preliminary Inflow Hydrology-Estimates of average monthly site inflows wili be generated
for each site based on regional studies by the USGS and on previous assessments of basin
water resources. These inflow estimates will provide an idea of the potential physical yield of
the site. The potential that water might be imported from other study area sub-basins or the
mainstem will be considered. More detailed hydrology will be developed in Sub-task 4c for
sites considered in project alternatives.

2) Site Reservoir Engineering-Storage volume estimates for each site will be derived based
on USGS 1:24000-scale maps (or other more detailed mapping, if available) and on previous
studies of the site, if any. Other indicators of construction requirements, such as
embankment length or length/height ratio, may also be developed. Because selection (Sub-
task 3c) will be based only on major "fatal flaws", more detailed engineering information,
such as spillway requIrements, land acquisition requirements, availability of construction
material, sediment production of the tributary basin, and site access will not be developed in
this sub-task. Existing Information which addresses these considerations will be considered
in determining engineering feasibility.

3) Geotechnical Flaws-Geotechnical flaws will be defined from USGS and CGS geologic
maps and SCS soil surveys, information from previous studies, review of aerial photographs,
and discussions with TSC members, knowledgeable local residents and professionals.
Obvious geotechnical and geologic fatal flaws which would significantly impact feasibility of
each site include proximity to active faults and liquefiable soils, presence oflandslides, sink
holes or cavernous limestone in the reservoir area, proximity to significant coal beds or other
minlng activities, presence of soluble rock formations or highly permeable solis, and
occurrence of moisture-sensitive soils.

4) Environmental Flaws-In general, only extraordinary environmental impacts will be
considered fatal. Identification of extraordinary environmental impacts will rely on existing
environmental studies and mapping and discussions with TSC members, knowledgeable local
residents and agency staff.

5) Water Delivery Capability-The potential ability of a site to deliver water to meet demands
is a critical screenlng criterion. This ability is a function of the potential water yield of the site
and the proximity of the site to preliminary water demands identified in Sub-task 2a.
Potential water yield will be estimated from site storage volume and average monthly inflow
estimates. The proximity of the site to water demands will be described in terms of required
water delivery and reservoir access facilities.